The invention concerns a unit for regulating or controlling a fluid pressure, in particular for the pressure regulation of the internal combustion engine and/or of the crankcase of the internal combustion engine of a motor vehicle, and a method for fluid-tightly connecting a switching film with at least one housing part of the unit.
Pressure regulating valves are used, for example, in the venting line between crankcase and the intake manifold of an internal combustion engine. In this context, the task is to prevent the pressure or vacuum in the containers to be vented from rising beyond a predetermined value.
In internal combustion engines, blow-by gases occur that are generated in that combustion gases in the cylinder bypass the cylinder piston and reach the crankcase. These blow-by gases cause the pressure in the crankcase to rise which may result in leakages and escape of oil. In order to avoid a pressure increase and to discharge the blow-by gases in an environmentally friendly way, the latter are returned from the crankcase into the air intake manifold of the internal combustion engine. On the other hand, the specified vacuum value should not be significantly undershot because otherwise, due to leaks, undesired infiltration air would be sucked into the crankcase.
In case of the pressure regulating valves which are employed currently, usually an element is used that is known to a person of skill in the art also under the term “switching membrane” and is made of elastomer, frequently fluorosilicone rubber (FVMQ). These switching membranes are very flexible due to the specific properties of elastomers. As a function of the applied pressure ratios, this switching membrane opens or closes an opening in the pressure regulating valve. The pressure ratio results usually from the pressure difference between the applied pressure in a first chamber and the pressure present in a second chamber of the pressure regulating valve. The pressure in the first chamber can be, for example, equal to the atmospheric pressure. The switching membrane must react to minimal switching pressures in the magnitude of 1 to 250 mbar.
Blow-by gases in an internal combustion engine are comprised of uncombusted fuel proportions, motor oil proportions, and other pollutants which are produced during the combustion. These gases attack many elastomer types so that damages to the material property may occur. The components of these materials become brittle, porous, and cracked. When the switching films are damaged, the environmentally damaging blow-by gases reach directly the environment because the system is no longer seal-tight. The switching membrane of an elastomer is usually designed as a roll film in order to realize a certain stroke of the switching membrane. The material in the rolling region is mechanically loaded by the rolling movement, while simultaneously being contacted by blow-by gases, and can thus be damaged.
DE 26 29 621 A1 discloses a membrane valve with a switching membrane which is embodied as a switching film clamped at its rim between the housing and the housing cover and, by means of a pressure member, is to be brought into sealing contact on a seat surface provided in the housing, wherein the switching membrane is comprised of a thinner layer of minimal elasticity, for example, of PTFE, that is facing the housing interior and is resistant against aggressive flow media, and comprised of a further thicker layer of elastic rubber material. Such membrane valves are used primarily where a high chemical resistance of the materials coming into contact with the flow medium is required. Since elastic rubber materials do not fulfill this requirement and the chemically resistant materials such as PTFE do not have the required elasticity for proper functioning, films comprised of two layers are employed. By means of the thick rubber-like layer, the contact pressure exerted by the pressure member is transmitted as uniformly as possible to the sealing surface of the switching film interacting with the seat surface in the housing. In this context, for closing the two-layer switching membrane, relatively great switching pressures of several bar are exerted on the switching membrane by a pressure spindle connected with a handwheel in order to ensure the required sealing function by means of the stiff PTFE layer.